im running a dell dimensions 3400 with windows xp yes i know its old but it gets the job done well did till this started i have no clue on what is going on or how to fix this i lost my windows xp install disc also so can't do anything from there
If the drive is unmountable it may have failed. Most Dells have a diagnostics routine that you can access by starting it up and pressing F12 while the Dell logo is displayed. Diagnostics, or in some cases, a Utility partition should be selectable from that menu. If you have it, try running the diagnostics to see if you get errors from the hard drive.
You will need the installation disk for the operating system to do anything, either to repair your installation or to reinstall the operating system. If you live in the U.S. you may be able to get a replacement installation disk by filling out this form: Dell Replacement Disk. If you live outside the U.S. you will need to contact Dell Technical Support for your region and ask them for the disk. Use the form in the link as a guide to the information you will need to supply to the Dell representative.